1. Field of the Invention
The present invention pertains in general to a filter and, more particularly, to an integrated filter with both common-mode and differential-mode functions.
2. Description of the Related Art
For an electric power circuit, electromagnetic interference (hereafter called EMI) signals are unavoidably generated by the on-off switching operations of the power line. These EMI signals are generally classified into radiation-type and conductive-type. In addition, the conductive-type EMI signal includes a differential-mode component and a common-mode noise component, respectively. These EMI signals do not only affect the operation of the circuit itself, but also influence the working of other electronic equipment by radiation or conduction. It is therefore necessary to take steps to suppress this interference.
FIGS. 1A and 1B (Prior Art) illustrate an example of various types of EMI signals and their propagation schemes. A conventional filter with differential-mode and common-mode functions can be separated into a common-mode filter and a differential-mode filter. As shown in FIGS. 1A and 1B, the common-mode filter is comprised of inductor L101 and inductor L102. In addition, the differential-mode filter is comprised of inductor L103 and an inductor L104. FIG. 1A illustrates the propagation scheme of common-mode interference signals. These interference signals are generated between wires and the ground. This kind of interference signal is referred to as common-mode since it has the same phases and amplitudes. FIG. 1B (Prior Art) illustrates the propagation scheme of differential-mode interference signals. This kind of interference signal is generated between two wires and referred to as differential-mode. Generally speaking, inductor L101 and inductor L102 have larger inductance values to suppress common-mode interference signals. Inductors L101 and L102, shown in the figure, are common-mode inductors wound on the same magnetic core. In addition, inductors L103 and L104 are serially connected to the circuit for suppressing the differential-mode interference signals.
The conventional filter as shown in FIGS. 1A and 1B is implemented by separated common-mode filters and differential-mode filters. Currently, there is a proposal to integrate common-mode filtering inductors and differential-mode filtering inductors into a magnetic core. FIG. 2 (Prior Art) illustrates the structure of a conventional integrated filter, developed by Motorola. The magnetic core thereof comprises E-shaped core 201, I-shaped core 202 and two coils 203 and 204 wound on the I-shaped core 202. The symbols "PHgr"DM and "PHgr"CM represent the magnetic flux of the differential-mode signal and the magnetic flux of the common-mode signal, respectively. The advantage of such a structure is its use of only one winding frame, wherein two coils can be wound on the same winding frame. The common-mode and differential-mode inductance values can be adjusted by modulating three air gaps pertaining to magnetic branches of the E-shaped core 201. However, this magnetic core structure having air gaps therein may influence the common-mode inductance values since the air gaps in the route of magnetic fluxes of the common-mode signals are not zero. In addition, the routes of differential-mode flux "PHgr"DM and the common-mode flux "PHgr"CM partially overlap. Therefore, the common-mode inductance value may be influenced since the differential-mode flux "PHgr"DM decreases the effective permeability of the magnetic core.
FIGS. 3A and 3B (Prior Art) illustrate a conventional integrated filter developed by Magnetek and disclosed in the U.S. Pat. No. 5,731,666, which includes two embodiments. The first embodiment, as shown in FIG. 3A, is similar to that shown in FIG. 2 except that a U-shaped core 31 and an I-shaped core 50 are used to replace the E-shaped core. The I-shaped core is made of low-permeability material. FIG. 3B illustrates the second embodiment. The integrated inductor is composed of a circular core 310 and an I-shaped core 320. However, in these two embodiments, the I-shaped core must be mounted on the inside of the circular core or the U-shaped core, which complicates the fabrication and installation processes. In addition, it is inconvenient to wind coils on the circular core. Therefore, production efficiency will decrease.
FIGS. 4A and 4B (Prior Art) illustrate a conventional integrated filter developed by Powercube and disclosed in U.S. Pat. No. 5,319,343. The windings 64 and 68 and the windings 66 and 70 shown in FIG. 4A are a combination of differential-mode inductors 76 and 78 and common-mode inductors 74 and 72 shown in FIG. 4B. The winding 62 solely constitutes the differential-mode inductor. The advantage of this magnetic core structure and winding arrangement is that the winding on the center column does not interact with the windings on the upper and lower columns of the magnetic core and the magnetic flux on the center column is only associated with the winding 62. However, this proposal is still unfavorable to implementation.
Accordingly, the objective of the present invention is to provide an integrated filter with both common-mode and differential-mode functions that can be implemented with ease.
According to the above objective, the present invention provides an integrated filter with both common-mode and differential-mode functions, which comprises a magnetic core, two windings and a frame for installing the windings. The magnetic core further comprises a rectangular core and an I-shaped core. The frame is fixed to a column of the rectangular core. In addition, two windings are wound on the frame. The I-shaped core is placed across the interior opening of the rectangular core and between these two windings.
In another aspect of the invention, the present invention also provides an integrated filter with both common-mode and differential-mode functions. The integrated filter also comprises a magnetic core, two windings and a frame for installing the windings. The magnetic core includes a xcex8-shaped core and an I-shaped core. The xcex8-shaped core has an interior opening and a central column traversing the opening. The frame is fixed to the central column of the xcex8-shaped core. Two windings are then wound on the frame. The I-shaped core traverses the opening of the xcex8-shaped core and between two windings, and is perpendicular to the central column of the xcex8-shaped core.
In another aspect of the invention, the present invention also provides an integrated filter with both common-mode and differential-mode functions. The integrated filter also comprises a magnetic core, two windings and a frame for installing the windings. The magnetic core includes a xcex8-shaped core and an E-shaped core. The frame is fixed to a central column of the xcex8-shaped core. Two windings are then wound on the frame. The E-shaped core is upright located on the central column of the xcex8-shaped core. A button surface of the E-shaped core faces the central column of the xcex8-shaped core. A central column of the E-shaped core is between two windings.
In another aspect of the invention, the present invention also provides an integrated filter with both common-mode and differential-mode functions. The integrated filter also comprises a magnetic core, two windings and a frame for installing the windings. The magnetic core includes a xcex8-shaped core and an E-shaped core. The xcex8-shaped core has at least one opening and a central column traversing the openings. The frame is mounted on the central column of the xcex8-shaped core. Two windings are then wound on the frame. The E-shaped core traverses one of the openings of the xcex8-shaped magnetic core. A central column of the E-shaped core is located between the first winding and the second winding.
In another aspect of the invention, the present invention also provides an integrated filter with both common-mode and differential-mode functions. The integrated filter also comprises a magnetic core, two windings and a frame for installing the windings. The magnetic core includes a rectangular core and an E-shaped core. The E-shaped core is located on a side of the rectangular core. The frame is mounted on a column of the rectangular core. A central column of the E-shaped core is located between the first winding and the second winding.
In another aspect of the invention, the present invention also provides an integrated filter with both common-mode and differential-mode functions. The integrated filter also comprises a magnetic core, two windings and a frame for installing the windings. The magnetic core includes a rectangular core and an E-shaped core. The rectangular magnetic core has an opening. The E-shaped magnetic core traverses the opening of the rectangular magnetic core. The frame is mounted on a column of the rectangular magnetic core. A central column of the E-shaped magnetic core is located between the first winding and the second winding.
As described above, the advantage of this structure is in the implementation.